The present invention relates to an apparatus for attaching threaded fasteners to a workpiece, which usually will have a first side, for which access is available, and a second side, which may be a blind side where access is not available. More particularly, this invention relates to a threaded insert having structural features which increase the resistance of the insert from spinning within the workpiece.
It is known to use threaded rivet nuts or threaded inserts as anchors for threaded fasteners in a number of different applications, including thin wall applications, such as sheet materials fabricated from metals, plastics and composites, which may be too thin to be tapped with threads. In many cases, there is access only to one side of the workpiece, which are known as “blind” applications. In general, the workpiece is drilled or punched and the anchor device is placed within the resulting hole by an installation tool. When the installation tool is activated, a portion of the anchor device on the blind side of the workpiece is deformed to create an enlargement which prevents removing the device from the hole. After the installation tool is removed, a threaded fastener may be inserted into a threaded portion of the device.
It is to be understood that the term “workpiece” as used in this specification refers to any material for which it is desirable to use any of the disclosed embodiments of this device. Typically, the materials for which the threaded insert has the greatest utility are blind applications for thin walled materials such as sheet metal or sheet plastic. Where there is only ready access to one side of a workpiece, it is necessary to employ anchors which may be completely deployed and installed on the visible side of the workpiece. As with other anchoring devices used in blind applications, the threaded insert must have features which retain the device within the workpiece and allow a threaded fastener to be inserted and tightened without the threaded insert spinning or rotating.
In addition, it is often desirable that the workpiece suffer minimal distortion when the threaded insert or fastener is installed to preserve the visual appeal of the workpiece. For example, if the workpiece comprises exposed panels of an automobile, it is desirable that the panels are not visibly deformed by the installation of threaded inserts and the related fasteners. Typically, a portion of the threaded insert on the blind side of the workpiece is plastically deformed into a bubble or secondary flange which is larger than the diameter of the hole in the workpiece, thereby preventing withdrawal of the threaded insert from the hole. It is desirable that the anchor device resist spinning or rotating within the hole and that the device be resistant to being pulled from the hole.